Electrostatic-erasing abrasion-proof coating and method for forming the same

ABSTRACT

An abrasion-proof and static-erasing coating is formed on the contact surface of a contact image sensor. The coating comprises a first film having a high hardness and a low conductivity, a second film formed on the first film and having a low hardness and a high conductivity, and a third film having a high hardness and a high resistivity providing an abrasion-proof insulating external surface.

This is a Divisional application of Ser. No. 08/016,240, filed Feb. 11, 1993; which itself is a division of Ser. No. 07/660,949, filed Feb. 26, 1991 (now U.S. Pat. No. 5,190,824); which itself is a continuation-in-part of Ser. No. 07/318,546 filed Mar. 3, 1989, abandoned.

BACKGROUND OF THE INVENTION

This invention relates to an electrostatic erasing abrasion-proof coating and method for forming the same.

Abrasion-proof coatings are formed over surfaces which has a tendency to take scratches due to external rubbing actions. The surface of glass plates which may be used for transmitting light therethrough is a typical example of such a surface. Contact image sensor, which have been recently developed, are suitable for use in compact facsimile machines, copying machines or the like. The image sensor makes direct contact with an original and scans the surface of the original by moving relative to this.

An example of the contact image sensor is illustrated in FIG. 1. The sensor comprises a glass substrate 1, a photosensitive semiconductor device 2, a transparent protective layer 3, an adhesive layer 4, an ITO film 5 and a glass pane 6. An original bearing an image to be sensed is placed in contact with the external surface of the glass pane 6. The ITO film, which is a transparent conductive film, is grounded for the purpose of canceling out electrostatic charges collected on the contact surface of the pane 6 due to rubbing action between the original 9 and the glass pane 6. In case of treatment of usual papers, the size of scratches may be of the order of 1 micron meter or less so that the performance of the sensor is not substantially deteriorated by the scratches. However, if a staple is held to a paper to be telefaxed, the paper, may give scratches of substantial size which degrade the quality of the transmission. Furthermore, the use of the ITO film for canceling out static electricity increases the size and the production cost of the device.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide art excellent abrasion-proof coatings and methods for forming the same which produce no static electricity on the coating even where rubbing action takes place thereon.

In order to accomplish the above and other objects, it is proposed to coat a surface with carbon films in different is deposition conditions in order that the external surface of the coating has a higher degree of hardness for providing art abrasion-proof surface and that the carbon coating includes art inner layer whose resistivity is comparatively low (conducting) to extinguish the influence of static electricity. This structure can be realized by inverting the polarity of the pair of electrodes, between which direct or high frequency electric energy is supplied, an object to be coated being mounted on one of the electrodes. When the electrode supporting the object is supplied with high frequency energy (that is to say, the electrode functions as the cathode), the hardness of carbon material becomes high. On the other hand, when the electrode supporting the object is grounded (i.e., the electrode functions as an anode), the hardness becomes low but the conductivity thereof becomes high. By letting the surface be a cathode, carbon material being deposited is eliminated due to bombardment of positive ions such as hydrogen ions, where the elimination rate of soft carbon material is higher than that of hard carbon material.

According to a preferred embodiment of the present invention, the energy band gap of carbon product for forming the external abrasion-proof surface of the coating is not lower than 1.0 eV, preferably 1.5 to 5.5 eV: the Vickers hardness is not lower than 500 Kg/mm², preferably not lower than 2000 Kg/mm², ideally not lower than 6500 Kg/mm², at the external surface of carbon coatings: the resistivity ranges from 10¹⁰ to 10¹⁵ ohm centimeter: and the thermal conductivity of the product is not. lower than 2.5W/cm deg, preferably 4.0 to 6.0W/cm deg. When used for thermal heads or contact image sensor which are frequently subjected to rubbing action, the smooth, hard and static erasing surface of the carbon coating is very suitable. The carbon coating includes an inner layer region having a low resistivity, The Vickers hardness and the resistivity of the inner layer region are not higher than 1000 Kg/mm² ₁ preferably 500 to 700 Kg/mm², and not higher than 10¹² ohm centimeter, preferably 1×10² to 1×10⁶ ohm centimeter. The inner layer region has lower Vickers hardness and higher conductivity than the external surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing a prior art contact image sensor.

FIG. 2 is a schematic diagram showing a CVD apparatus for depositing carbon material in accordance with the present invention.

FIG. 3 is a graphical diagram showing the Vickers hardness and the resistivity of carbon films which have been deposited on an electrode functioning as a cathode.

FIG. 4 is a graphical diagram showing the Vickers hardness and the resistivity of carbon films which have been deposited on an electrode functioning as an anode.

FIG. 5 is a schematic diagram of a carbon coating in accordance with the present invention.

FIGS. 6(A), 6(B), 7(A), 7(B), 8(A), and 8(B) are graphical diagrams showing the variations of the hardness and the resistivity of carbon films through the depth thereof in, accordance with the present invention.

FIG. 9 is a cross sectional view showing an image sensor given a carbon coating in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 2, there is shown a plasma CVD apparatus for depositing carbon material on a surface in accordance with the teaching of the present invention. The surface to be coated may, for example, be made of semiconductor, glass, metal, ceramics, organic resins, magnetic substance, and so forth.

The apparatus comprises a reaction chamber 18 defining a reaction space 30 therein, first and second electrodes 21 and 22, a high frequency electric power source 23 for supplying electric power between the electrodes 21 and 22 through a matching transformer 24, a DC bias source 25 connected in series between the electrodes 21 and 22, a gas feeding system 11 consisting oil four passages 12 to 15 each of which is provided with a flow meter 17 and a valve 16, a microwave energy supply 20, a nozzle 19 through which gas excited by the microwave energy supply 20 is introduced into the reaction space 30, and an exhaust system 26 including a pressure control valve 27, a turbomolecular pump 28 and a rotary pump 29. The electrodes are designed such that (the area of the first electrode 21)/(the area of the second electrode 22)<1. A pair of switching means 31 and 32 is provided for inverting the polarities of the electrodes 21 and 22. In a first position of the switching means, the electrode is grounded while the other electrode 21 is supplied with high frequency electric energy from the power source 23. In the other second position, the electrode 21 is grounded while the electrode 22 is supplied with high frequency electric energy from the power source 23. An object having the surface to be coated is mounted on the electrode 21.

In operation of this apparatus, a carrier gas of hydrogen is introduced to the reaction space 30 from the gas feeding passage 12 as well as a reactive gas of a hydrocarbon such as methane or ethylene from the gas feeding passage 13. The gas introduction rates of hydrogen and the hydrocarbon are 3:1 to 1:3, preferably 1:1. In addition to this, a V-Group dopant gas such as NH₃ or PH₃, or a III-Group dopant gas may be inputted to the reaction space 30 through the gas feeding passage 14 or 15 in order to form impurity semiconductors. Pre-excitation may be effected by the microwave energy supply 10. The pressure in the reaction space is maintained within the range between 0.001 to 10) Torr, preferably 0.01 to 0.5 Torr. High frequency electric energy at a frequency not lower than 1 GHz, e.g. 2.45 GHz, is applied to the reactive gas at 0.1 to 5 kilo Watt for breaking C—H bonds. When-the frequency is selected to be 0.1 to 50 MHz, C═C bonds can be broken and transformed to —C—C— bonds. By virtue of this reaction, carbon atoms are deposited atoms in the form of a structure in which the diamond structure occurs at least locally.

A bias voltage of, for example, −200 to 600 V is set at the DC bias source 15. The effective bias voltage level is substantially −400 to +400 V when a self bias level in this case of −200 V is spontaneously applied between the electrodes 21 and 22 with the bias voltage level of the source 15 being zero.

Generally, the high frequency input power is chosen between 10 Watt and 5 kilo Watt, preferably between 50 Watt and 1 kilo Watt. This input power corresponds to 0.03 to 3 Watt/cm² in terms of plasma energy. The substrate temperature is maintained in a range of +250 to −100° C. by means of a temperature control means (not shown). When diamond deposition is desired, the substrate temperature has to be elevated further.

FIG. 3 shows the resistivity and the Vickers hardness of films deposited on a surface, to which high frequency electric: energy was applied through the electrode 21 at various power levels. As can be seen from the figure, a harder film was deposited by inputting higher power energy. FIG. 4 shows the resistivity and the Vickers hardness of films deposited on a surface which was grounded. Comparing FIG. 4 with FIG. 3, it will be apparent that the resistivity of carbon films formed at the anode side (on the grounded electrode) becomes lower than that in the cathode side (supplied with high frequency energy).

In accordance with the teaching of the present invention, a surface is coated with a carbon coating while the deposition condition is changed in order that the hardness of the carbon initially or intermediately deposited on the substrate is relatively low, but the deposition condition is changed such that hardness of the carbon finally deposited becomes very high in order to provide a hard external abrasion-proof surface. This procedure can be carried out in two ways. As seen from FIG. 6(A), the hardness may be changed in steps by stepwise change of the deposition condition in accordance with the above description. Alternatively, as seen from FIG. 6(B), the hardness may be changed continuously from the inner surface to the external surface of the carbon coating.

The hardness or resistivity of the carbon coating can be changed, rather than monotonically, in order that an intermediate region of the coating is conductive and sandwiched by hard carbon regions. FIG. 5 illustrates such a case including three carbon film regions. The lower and top films 41 and 43 are deposited to have a high degree of hardness while the intermediate film 42 is deposited to have low resistivity. This example can be realizes in two ways as illustrated in FIG. 7 (stepwise change) and FIG. 8. (continuous change). The lower hard film 41 is semi-insulating so that it protects the surface to be coated electrically and mechanically. Further the lower hard film has a function as a blocking layer to prevent impurity from entering into the intermediate film 42 and also a function of improving adhesivity to the substrate and the electrical property. The intermediate region 42 has conductivity and functions as a Buffer layer to alleviate distortion generated by mechanical stress.

Experiment 1

A carbon coating was deposited on a transparent polyimide film 35 as shown in FIG. 9. An amorphous silicon photosensitive semiconductor device 34 was formed on a glass substrate 33 in a conventional manner as well as the polyimide film 35. A first carbon film 36 of 0.6 micron meter thickness was formed on the polyimide film 35 under deposition conditions that the structure was placed on the electrode (cathode) supplied with high frequency energy of 260 W, the introduction rate of carbide gas such as methane, ethylene, or ethane diluted by hydrogen (e.g. methane:hydrogen=1:1) was 100SCCM, the pressure of the reactive gas was 0.03 Torr, and the deposition time was 60 minutes. The hardness and the resistivity were measured to be 1000 Kg/mm² and 1×10¹² ohm centimeter. A second carbon film 37 of 0.5 micron meter thickness was formed on the first film 36 under deposition conditions that the electrode supporting the structure was grounded (as an anode), the input high frequency energy was 300 W, the introduction rate of carbide gas such as methane, ethylene, or ethane diluted by hydrogen (e.g. methane:hydrogen=1:1) was 100SCCM, the pressure of the reactive gas was 0.03 Torr, and the deposition time was 40 minutes. The hardness and the resistivity were measured to be 600 Kg/mm² and 1×10¹⁰ ohm centimeter. Finally, a third carbon film 38 was deposited in the same deposition conditions as the first film 36. The first film may be dispensed with.

Experiment 2

This was carried out in accordance with the diagram shown in FIGS. 8(A) and 8(B) rather than FIGS. 7(A) and 7(B). That is, the resistivity and the hardness were continuously decreased and M increased along with the decrease and the increase of input energy. Carbon deposition was started under the deposition conditions that the structure was placed on the electrode (cathode) supplied with high frequency energy of 300 W, the introduction rate of carbide gas such as methane, ethylene, or ethane diluted by hydrogen (e.g. methane:hydrogen=1:1) was 100SCCM, and the pressure of the reactive gas was 0.03 Torr. The input high frequency energy was gradually decreased from 300 W to 200 W at 0.5 to 2.5 W/min. The hardness and the resistivity were decreased, along with the decrease of the input energy, from 1000 Kg/mm² to 500 Kg/mm² and from 1×10¹² ohm centimeter to not lower than 1=10⁸ ohm centimeter respectively. The total thickness of this carbon coating was 0.2 micron meter. After the positions of the switch 31 and 32 were reversed (i.e. the electrode 21 was grounded as an anode), carbon deposition was resumed while the input power was decreased from 300W to 200W and subsequently increased from 200W to 300W at 0.5 to 2.5 W/min. The hardness and the resistivity were changed along with the change of the input energy, that is, the hardness was decreased from 500 Kg/mm² to 300 Kg/mm² and subsequently increased from 300 Kg/mm² to 500 Kg/mm² and the resistivity was decreased and then increased within the range between 1×10¹² ohm centimeter and 1×10⁸ ohm centimeter. However, the resistivity of this intermediate layer should be lower than that of the underlying hard carbon coating as illustrated in FIGS. 8(A) and 8(B). The total thickness of this carbon coating was 0.4 to 1 micron meter. After the positions of the switch 31 and 32 were reversed again in the initial positions (i.e. the electrode 21 was supplied with high frequency energy as a cathode), carbon deposition was resumed while the input power was increased from 200 W to 300 W at 0.5 to 2.5 W/min. The hardness and the resistivity were increased, along with the input energy, from 500 Kg/mm² to 2000 Kg/mm² and from not lower than 1×10⁸ ohm centimeter to 1×10¹² ohm centimeter. However, the resistivity of this upper carbon film should be higher than that of the intermediate layer. The total thickness of this carbon coating was 0.3 to 0.7 micron meter.

Experiment 3

A first carbon film of 0.6 micron meter thickness was formed on the polyimide film under deposition conditions that the structure was placed on the electrode (cathode) supplied with high frequency energy of 260 W, the introduction rate of carbide gas such as methane, ethylene, or ethane diluted by hydrogen (e.g. methane:hydrogen=1:1) was 100SCCM, the pressure of the reactive gas was 0.03 Torr, and the deposition time was 60 minutes. The hardness and the resistivity were measured to be 1000 Kg/mm² and 1×10¹² ohm centimeter. A second carbon film of 0.5 micron meter thickness was formed on the first film under deposition conditions that the electrode supporting the structure was grounded (as an anode), the input high frequency energy was 300 W, the introduction rate of carbide gas such as methane, ethylene, or ethane diluted by hydrogen was 100 SCCM, the pressure of the reactive gas was 0.03 Torr, and the deposition time was 40 minutes. The hardness and the resistivity were measured to be 600 Kg/mm² and 1×10¹⁰ ohm centimeter. On the second film, a third external film was deposited at an input energy of 80 W for 50 min., at 150 W for 50 min. and at 300 W for 40 min sequentially. Then the third film was formed, having its resistivities of 5×10¹⁰, 2×10¹², and 1×10¹⁴ ohm centimeter across its thickness of 1.7 micron meters.

Experiment 4

A first carbon film of 0.6 micron meter thickness was formed on the polyimide film under deposition conditions that the structure was placed on the electrode (cathode) supplied with high frequency energy of 260 W, the introduction rate of carbide gas such as methane, ethylene, or ethane diluted by hydrogen (e.g. methane:hydrogen=1:1) was 100SCCM, the pressure of the reactive gas was 0.03 Torr, and the deposition time was 60 minutes. The hardness and the resistivity were measured to be 1000 Kg/mm² and 1×10¹² ohm centimeter. After the positions of the switch 31 and 32 were reversed (i.e. the electrode 21 was grounded as an anode), a second carbon film was formed while the input power was decreased from 300W to 200W and subsequently increased from 200W to 300W at 0.5 to 2.5 W/min. The hardness and the resistivity were changed along with the change of the input energy, that is, the hardness was decreased from 500 Kg/mm.² to 300 Kg/mm² and subsequently increased from 300 Kg/mm² to 500 Kg/mm² and the resistivity was decreased and then increased within the range between 1×10¹² ohm centimeter and 1×10⁸ ohm centimeter. However, the resistivity of this second carbon film should be lower than that of the first carbon film. The total thickness of this carbon coating was 0.4 to 1 micron meter. On the second film, a third external film was deposited at an input energy of 80 W for 50 min., at 150 W for 50 min. and at 300 W for 40 min. sequentially. Then the third film was formed, having its resistivities of 5×10¹⁰, 2×10², and 1×10¹⁴ ohm centimeter across its thickness of 1.7 micron meters.

Experiment 5

First and third carbon films were deposited in diamond structure. The deposition conditions required to deposited carbon crystals (diamond) were 700 to 900° C. (substrate temperature), 1.0 to 5 KW (input high frequency energy), 12 hours (deposition time) and CH₄/H₂=0.1 to 4 (reactive gas), 3 to 80 Torr (pressure). The thickness of the first and third films were 0.6 micron meter respectively. The Vickers hardness was measured to be 10,000 Kg/mm². The resistivity was 1×10¹⁵ ohm centimeter. After the first film deposition, a second carbon film (i.e. intermediate film) of 0.5 micron meter thickness was formed on the first film under deposition conditions that the electrode supporting the structure was grounded (as an anode), the input high frequency energy was 300 W, the introduction rate of methane diluted by hydrogen was 100SCCM, the pressure of the reactive gas was 0.03 Torr, and the deposition time was 40 minutes. The hardness and the resistivity were measured to the 600 Kg/mm² and 14×10¹⁰ ohm centimeter. Subsequently, the third film was formed under the above deposition conditions.

While a description has been made for several embodiments, the present invention should be limited only by the appended claims and should not be limited by the particular examples, and there may be caused to artisan some modifications and variation according to the invention. For example, it has been proved effective to add hydrogen, a halogen, boron, nitrogen, phosphorus or the like into the carbon coating. Preferably, the proportion of hydrogen or a halogen is not higher than 25 atomic % and the proportion of the other additives are not higher than 5%. Also, though the experiments were carried out for depositing carbon coatings on semiconductor substrates, the carbon coatings can be deposited on a substrate made of an organic resin such as PET (polyethyleneterephtalen), PES, PMMA, teflon, epoxy and polyimides, metallic meshes, papers, glass, metals, ceramics, parts for magnetic heads, magnetic discs, and others.

The types of carbon coatings deposited in accordance with the present invention includes amorphous, polycrystals (comprising diamond powders), and diamond films. In the case of a dual film, lower and upper films may be, respectively, amorphous and amorphous (having different hardnesses), amorphous and polycrystals, polycrystals and polycrystals, or polycrystals and a diamond film. 

What is claimed is:
 1. A method for manufacturing an article comprising a ceramic surface being coated with an amorphous carbon coating, wherein said carbon coating has C—C bonds and contains hydrogen, said method comprising the steps of: introducing a reactive gas comprising a carbon containing gas into a reaction chamber; supplying an electrical energy to the reactive gas to generate a plasma; depositing said amorphous carbon coating having C—C bonds on said ceramic surface through plasma CVD from said plasma, wherein a hardness of said amorphous carbon coating monotonically increases from a first point close to said ceramic surface to a second point more distant from said surface than said first point.
 2. A method according to claim 1 wherein a temperature of said ceramic surface is maintained within a range from −100 to 250° C. during the deposition.
 3. A method according to claim 1 wherein said electrical energy has a frequency from 0.1 MHz to 50 MHz.
 4. A method according to claim 1 wherein said reactive gas contains a dopant gas for adding a group IIIA element.
 5. A method according to claim 1 wherein said reactive gas contains a dopant gas selected from the group consisting of NH₃ and PH₃.
 6. A method according to claim 1 wherein said amorphous carbon coating contains an element selected from the group consisting of a halogen element, phosphorus, boron and nitrogen.
 7. A method according to claim 1 wherein said amorphous carbon coating contains hydrogen or a halogen element at a concentration not higher than 25 atomic %.
 8. A method according to claim 1 wherein said amorphous carbon coating contains P, B or N at a concentration not higher than 5%.
 9. A method according to claim 1, wherein the ceramic surface is located on an electrode which is supplied with an effective bias voltage from −400 to 400V.
 10. A method according to claim 1 wherein said hardness increases in a stepwise manner.
 11. A method according to claim 1 wherein said hardness increases continuously.
 12. A method for manufacturing an article comprising a ceramic surface being coated with an amorphous carbon coating, wherein said carbon coating has C—C bonds and contains hydrogen, said method comprising the steps of: introducing a reactive gas comprising a carbon containing gas into a reaction chamber; supplying a microwave electrical energy to the reactive gas; and depositing said amorphous carbon coating on said ceramic surface, wherein a hardness of said amorphous carbon coating monotonically increases from a first point close to said ceramic surface to a second point more distant from said surface than said first point.
 13. A method according to claim 12 wherein a temperature of said ceramic surface is maintained within a range from −100 to 250° C. during the deposition.
 14. A method according to claim 12 wherein said reactive gas contains a dopant gas for adding a group IIIA element.
 15. A method according to claim 12 wherein said reactive gas contains a dopant gas selected from the group consisting of NH₃ and PH₃.
 16. A method according to claim 12 wherein said amorphous carbon coating contains an element selected from the group consisting of a halogen element, phosphorus, boron and nitrogen.
 17. A method according to claim 12 wherein said amorphous carbon coating contains hydrogen or a halogen element at a concentration not higher than 25 atomic %.
 18. A method according to claim 12 wherein said amorphous carbon coating contains P, B or N at a concentration not higher than 5%.
 19. A method according to claim 12 wherein said microwave electrical energy is a high frequency power having a frequency not lower than 1 GHz.
 20. A method according to claim 12 wherein said hardness increases in a step-wise manner.
 21. A method according to claim 12 wherein said hardness increases continuously.
 22. A method for manufacturing an article comprising: a ceramic surface; a protective film formed on the ceramic surface, said protective film including, an upper layer comprising an amorphous carbon coating having C—C bonds, an underlying layer being interposed between the ceramic surface and the uppermost layer, said method comprising the steps of: introducing a reactive gas comprising a carbon containing gas into a reaction chamber; supplying an electrical energy to the reactive gas to generate a plasma; and forming the upper layer on said underlying layer through plasma CVD from the plasma, wherein a hardness of said protective film monotonically increases from a first point close to said ceramic surface to a second point from distant from said ceramic surface than said first point and at least said upper layer contains hydrogen or a halogen element at a concentration not higher than 25 atomic %.
 23. A method according to claim 22 wherein at least said upper layer contains an element selected from the group consisting of hydrogen, a halogen element, phosphorus, boron and nitrogen.
 24. A method according to claim 22 wherein said upper layer has Vickers hardness not lower than 2000 kg/mm².
 25. A method according to claim 22 wherein at least said upper layer contains P, B or N at a concentration not higher than 5%.
 26. A method according to claim 22 wherein said underlying layer comprises carbon.
 27. A method according to claim 22 wherein a Vickers hardness of the underlying layer is smaller than that of the upper layer.
 28. A method according to claim 12 wherein said hardness increases in a step-wise manner.
 29. A method according to claim 22 wherein said hardness increases continuously.
 30. A method for manufacturing an article comprising: a ceramic surface; a protective film formed on the ceramic surface, said protective film including, an upper layer comprising an amorphous carbon coating having C—C bonds, an underlying layer being interposed between the ceramic surface and the uppermost layer, said method comprising the steps of: introducing a reactive gas comprising a carbon containing gas into a reaction chamber; supplying a microwave electrical energy to the reactive gas; and forming the upper layer on said underlying layer wherein said upper layer has a Vickers hardness not lower than 2000 kg/mm²and wherein a hardness of said protective film monotonically increases from a first point close to said ceramic surface to a second point more distant from said ceramic surface than said first point.
 31. A method according to claim 30 wherein at least said upper film contains an element selected from the group consisting of hydrogen, a halogen, element, phosphorus, boron and nitrogen.
 32. A method according to claim 30 wherein at least said upper film contains hydrogen or a halogen element at a concentration not higher than 25 atomic %.
 33. A method according to claim 30 wherein at least said upperfilm contains P, B or N at a concentration not higher than 5%.
 34. A method according to claim 30 wherein said underlying layer comprises carbon.
 35. A method according to claim 30 wherein a Vickers hardness of the underlying layer is smaller than that of the upper layer.
 36. A method according to claim 30 wherein said hardness increases in a step-wise manner.
 37. A method according to claim 30 wherein said hardness increases continuously.
 38. A method for manufacturing an article comprising: a ceramic surface; a protective film formed on the ceramic surface, said protection film including, a diamond like carbon film comprising an amorphous carbon coating having C—C bonds, an adhesive layer being interposed between the ceramic surface and the diamond like carbon film, said method comprising the steps of: introducing a reactive gas comprising a carbon containing gas into a reaction chamber; supplying an electrical energy to the reactive gas to generate a plasma; and forming the diamond like carbon film on said adhesive layer through plasma CVD from the plasma, wherein a hardness of said protective film monotonically increases from a first point close to said ceramic surface to a second point more distant from said ceramic surface than said first point.
 39. A method according to claim 38 wherein at least said diamond like carbon film contains an element selected from the group consisting of hydrogen, a halogen element, phosphorus, boron and nitrogen.
 40. A method according to claim 38 wherein at least said diamond like carbon film contains hydrogen or a halogen element at a concentration not higher than 25 atomic %.
 41. A method according to claim 38 wherein at least said diamond like carbon film contains P, B or N at a concentration not higher than 5%.
 42. A method according to claim 38 wherein said adhesive layer comprises carbon.
 43. A method according to claim 38 wherein said a Vickers hardness of the adhesive layer is smaller than that of the diamond like carbon film.
 44. A method according to claim 38 wherein said hardness increases in a step-wise manner.
 45. A method according to claim 38 wherein said hardness increases continuously.
 46. A method for manufacturing an article comprising: a ceramic surface; a protective film formed on the ceramic surface, said protective film including, a diamond like carbon film comprising an amorphous carbon coating, an adhesive layer being interposed between the ceramic surface and the diamond like carbon film, said method comprising the steps of: introducing a reactive gas comprising a carbon containing gas into a reaction chamber; supplying a microwave electrical energy to the reactive gas; and forming the diamond like carbon film on said adhesive layer, wherein a hardness of said protective film monotonically increases from a first point close to said ceramic surface to a second point more distant from said ceramic surface than said first point.
 47. A method according to claim 46 wherein at least said diamond like carbon film contains an element selected from the group consisting of hydrogen, a halogen element, phosphorus, born and nitrogen.
 48. A method according to claim 46 wherein at least said diamond like carbon film contains hydrogen or a halogen element at a concentration not higher than 25 atomic %.
 49. A method according to claim 46 wherein at least said diamond like carbon film contain P, B or N at a concentration not higher than 5%.
 50. A method according to claim 46 wherein said adhesive layer comprises carbon.
 51. A method according to claim 46 wherein a Vickers hardness of the adhesive layer is smaller than that of the diamond like carbon film.
 52. A method according to claim 46 wherein said hardness increases in a step-wise manner.
 53. A method according to claim 46 wherein said hardness increases continuously.
 54. A method for manufacturing an article comprising: a ceramic surface; a protective film formed on the ceramic surface, said protective film including, a diamond like carbon film composing an amorphous carbon coating, an adhesive layer being interposed between the ceramic surface and the diamond like carbon film, said method comprising the steps of: introducing a reactive gas comprising a carbon containing gas into a reaction chamber; supplying a microwave electrical energy to the reactive gas; supplying a second electrical energy to the reactive gas to generate a plasma; forming the adhesive layer on said ceramic surface; and forming the diamond like carbon film on said adhesive layer through plasma CVD from the plasma, wherein a hardness of said protective film monotonically increases from a first point close to said ceramic surface to a second point more distant from said ceramic surface than said first point.
 55. A method according to claim 54, wherein at least said diamond like carbon film contains an element selected from the group consisting of hydrogen, a halogen element, phosphorous, born and nitrogen.
 56. A method according to claim 54, wherein at least said diamond like carbon film contains hydrogen or a halogen element at a concentration not higher than 25 atomic %.
 57. A method according to claim 54, wherein at least said diamond like carbon film contains P, B or N at a concentration not higher than 5%.
 58. A method according to claim 54, wherein said second electrical energy is a high frequency power having a frequency from 0.1 MHz to 50 MHz.
 59. A method according to claim 54, wherein said microwave electrical energy is a high frequency power having a frequency not lower than 1 GHz.
 60. A method according to claim 54, wherein said adhesive layer comprises carbon.
 61. 4 method according to claim 54, wherein a Vickers hardness of the adhesive layer is smaller than that of the diamond like carbon film. 